We first heard about this earlier this week, when GigaOm’s Laura Hazard Owen surfaced promotional materials for the service. Now it’s out in the open.

As many wags have pointed out, Kindle Unlimited is in many ways a paid version of the free offerings everyone can already get from their local library. But it is also competing with Amazon’s own Kindle Owner’s Lending Library, the service Amazon bundles along with lots of other perks for Prime subscription owners.

Both of those services seem to offer the same catalog of some 600,000 books. But the paid service lets you read as many e-books as you want, on any device, while the free/Prime one is limited to one a month, and only on Kindles. The paid service also offers access to more than 2,000 audiobooks, and a three-month subscription to Audible, Amazon’s audiobook service.

In recent years Amazon has been trying to increase Prime’s appeal by adding more features to the shipping service — first, a video service that is getting increasingly attractive, and now a music service that isn’t blowing anyone away yet. What’s most interesting is that they’re making this new service a standalone, rather than throwing it into the Prime pot.